1. Field of the Invention
The present invention relates to a control apparatus for a hydraulically operated vehicular transmission having a plurality of speed stages to be established by a selecting operation of a plurality of hydraulic engaging elements. In this specification, the term "vehicular transmission" means a transmission for a vehicle such as a motor vehicle.
2. Description of the Related Art
As this kind of control apparatus, there has hitherto been known the following one. Namely, a hydraulic pressure of a hydraulic engaging element on a disengaging side to be disengaged at the time of speed changing (disengaging pressure) and a hydraulic pressure of a hydraulic engaging element on an engaging side to be engaged at the time of speed changing (engaging pressure) are electronically controlled by using solenoid proportional valves. Input and output speed ratio (rotational speed of an output shaft/rotational speed of an input shaft) of a transmission is detected and a discrimination is made of a condition of progress or development of speed changing based on the input and output speed ratio. Based on the result of this discrimination, the disengaging pressure and the engaging pressure are controlled to thereby perform a smooth speed changing. In this case, in order to enable to perform speed changing without giving rise to shocks even when the input and output speed ratio does not show a normal value, the disengaging pressure and the engaging pressure are normally controlled by jointly using the time of lapse from the start of speed changing as a controlling parameter.
When a different speed change command has been issued during the speed change control, it is desired to stop the speed change control that was in progress up to that time so that the speed change control to deal with the different speed change command can be performed immediately. In case one speed changing is switched over (or changed) to another speed changing in the midst of (or in the course of) speed changing as described above, the speed changing has already progressed to a certain extent by the preceding speed change control. Therefore, there will be no more relationship between the time of lapse from the start of speed changing and the condition of development of speed changing. As a result, in the switchover speed changing, it is no longer possible to obtain, by a control depending on the time of lapse from the start of speed changing, a correction function to be used when the input and output speed ratio does not show a normal value.
In view of the above-described point, the present invention has an object of providing a control apparatus in which a discrimination is made whether the input and output speed ratio is accurately detected and, when it is not accurately detected, the switchover speed changing is not performed, whereby the occurrence of shocks by the switchover speed changing can be prevented.